1. Field of the Invention
The present invention pertains to telecommunications, and particularly to the transmission of cell information between control nodes of a radio access network.
2. Related Art and Other Considerations
In a typical cellular radio system, mobile user equipment units (UEs) communicate via a radio access network (RAN) to one or more core networks. The user equipment units (UEs) can be mobile stations such as mobile telephones (“cellular” telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. The base stations communicate over the air interface (e.g., radio frequencies) with the user equipment units (UE) within range of the base stations. In the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
One example of a radio access network is the Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN). The UTRAN is a third generation system which is in some respects builds upon the radio access technology known as Global System for Mobile communications (GSM) developed in Europe. UTRAN is essentially a wideband code division multiple access (W-CDMA) system.
As those skilled in the art appreciate, in W-CDMA technology a common frequency band allows simultaneous communication between a user equipment unit (UE) and plural base stations. Signals occupying the common frequency band are discriminated at the receiving station through spread spectrum CDMA waveform properties based on the use of a high speed, pseudo-noise (PN) code. These high speed PN codes are used to modulate signals transmitted from the base stations and the user equipment units (UEs). Transmitter stations using different PN codes (or a PN code offset in time) produce signals that can be separately demodulated at a receiving station. The high speed PN modulation also allows the receiving station to advantageously generate a received signal from a single transmitting station by combining several distinct propagation paths of the transmitted signal. In CDMA, therefore, a user equipment unit (UE) need not switch frequency when handoff of a connection is made from one cell to another. As a result, a destination cell can support a connection to a user equipment unit (UE) at the same time the origination cell continues to service the connection. Since the user equipment unit (UE) is always communicating through at least one cell during handover, there is no disruption to the call. Hence, the term “soft handover.” In contrast to hard handover, soft handover is a “make-before-break” switching operation.
There are several interfaces of interest in the UTRAN. The interface between the radio network controllers (RNCs) and the core network(s) is termed the “Iu” interface. The interface between a radio network controller (RNC) and its base stations (BSs) is termed the “Iub” interface. The interface between the user equipment unit (UE) and the base stations is known as the “air interface” or the “radio interface”. In some instances, a connection involves both a Serving or Source RNC (SRNC) and a target or drift RNC (DRNC), with the SRNC controlling the connection but with one or more diversity legs of the connection being handling by the DRNC. The interface between a SRNC and a DRNC is termed the “Iur” interface. An understanding of the functions performed by the SRNC, the DRNC, and the type of information exchanged therebetween can be gleaned from one or more of the following (all of which are incorporated herein by reference) U.S. patent application Ser. No. 09/035,821 filed Mar. 6, 1998, entitled “Telecommunications Inter-Exchange Measurement Transfer”; U.S. patent application Ser. No. 09/035,788 filed Mar. 6, 1998, entitled “Telecommunications Inter-Exchange Congestion Control”; U.S. patent application Ser. No. 09/638,858 filed Aug. 15, 2000, entitled “Transfer of Overlapping Routing Area Control Information In A Radio Access Network”; and U.S. patent application Ser. No. 09/543,536 filed Apr. 5, 2000, entitled “Relocation of Serving Radio Network Controller With Signaling of Linking of Dedicated Transport Channels”.
When it is appropriate to establish a new leg of a connection controlled by a SRNC through a base station controlled by a DRNC, the SRNC typically requests that the DRNC allocate resources (e.g., radio link resources) for the new leg of the connection in the cell served by the base station which will host the new leg. The Third Generation Partnership Project (3GPP), which has undertaken to evolve further the UTRAN and GSM-based radio access network technologies, proposes in its specifications that the DRNC transmit or transfer cell information for each cell where radio resources are being established. See, e.g., 3G TS 25.423, v.3.4.0: UTRAN Iur Interface RNSAP Signaling (ftp://ftp.3gpp.org/Specs/2000-12R/R1999/25 series/25423-340.zip). The transfer of cell information as proposed by the 3GPP means that, if an SRNC requests resources in a particular cell for many users (UEs), the SRNC will in response receive the same cell information many times (once for each user) from the DRNC. Such redundancy is inefficient and consume unnecessary bandwidth in the signaling network and causes additional signaling delay.
What is needed, therefore, and an object of the present invention, is an efficient and economical technique for communicating cell information between radio network control nodes of a radio access network.